Disk drive devices using various kinds of disks, such as optical disks, magneto-optical disks, and flexible magnetic disks, have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of indispensable storage devices for current computer systems. Moreover, the HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, in addition to the computers, due to their outstanding characteristics.
In portable electronic equipment with a built-in HDD, protection of the HDD from an impact when the electronic equipment has accidentally fallen onto the ground, for example, is an important object. An HDD spins a magnetic disk and moves a head slider flying above the magnetic disk to a target data sector to access the magnetic disk. Therefore, if an impact is applied to an HDD in operation by a fall, a head slider, a suspension supporting the head slider, or a magnetic disk (data on the magnetic disk) may be damaged by the collision between the head slider and the magnetic disk.
To prevent such damage, a protection mechanism has been known that detects falling of an HDD or HDD built-in electronic equipment and withdraws a head slider to a safe position (stand-by position) where the head slider will not contact the magnetic disk. Typically, the HDD comprises a ramp where an actuator is to be withdrawn and moves the actuator onto the ramp when it has detected a fall. An HDD with such a protection mechanism mounted is disclosed in Japanese Patent Publication No. 2007-115309 (“Patent Document 1”), for example.
A head slider may collide with a magnetic disk because of an external impact as well as a fall. A typical HDD having a fall sensor comprises an impact sensor, too; when the impact sensor detects an impact, the HDD moves the actuator onto the ramp (refer to Japanese Patent Publication No. 2001-14783 “Patent Document 2”, for example). The timing of impact application from the external is irregular. On the other hand, an HDD may have different levels of impact resistance depending on the HDD's operation.
To this end, Patent Document 2 proposes to change the impact threshold to unload the actuator depending on the HDD's operation. For example, an HDD disclosed in Patent Document 2 adopts different thresholds between a seek operation and a following operation; if the HDD detects any impact exceeding the threshold corresponding to the operation, it stops the operation and unloads the actuator (head slider).
In a typical fall of an HDD, the HDD collides with a floor after a free fall. The HDD is required to unload the actuator after detecting the fall until the collision. Differing from a direct impact applied to the HDD, there exists a certain amount of fall duration from the beginning of the fall to the application of an impact to the HDD. Therefore, it is sufficient if the controller unloads the actuator from the beginning of the fall until the collision and the controller does not need to unload the actuator immediately after the beginning of the fall.
When the controller in an HDD interrupts host command processing, it needs to save many parameters to resume the process according to the occasions of the interrupt, which is a heavy load to the controller. Unloading operation in response to a fall with arbitrary timing during command processing may cause an error in the processing in the controller and reduce the safety in the controller's processing.
Accordingly, it may be desirable to conduct an unloading operation in response to a fall detection only on predetermined occasions in command processing. In an HDD which conducts an unloading operation when it has recognized a fall, the timing of the unloading operation can be limited to the intended timing in a process by restricting the timing for the controller to check for a fall.
The controller can proceed with command processing within the time lag between the beginning of a fall and the collision. Therefore, even if the occasions available for unloading in the process is restricted, setting appropriate occasions allows the controller to proceed with the process into a fall check before the HDD receives an impact by a collision to the floor, so that the controller can safely withdraw the head slider.
However, the duration from the beginning of a fall to the HDD's receipt of impact depends on the height of the fall. As more mobile products employ HDDs, securer protection operation against falls from lower height has been requested. To improve the HDD's safety against a fall and to achieve an actuator's unloading before a collision caused by a fall from a lower position, it is necessary to reduce the duration from the beginning of a fall to the controller's check for the fall.
In an HDD which unloads an actuator after checking for a fall, increase in frequency of the controller's check for a fall detection results in reduction of time intervals between the fall checks. This reduces a successive processing time without a fall check after the beginning of a fall to accomplish a more rapid unloading operation after the beginning of a fall.
However, newly setting the timing of fall check requires much time and large resources, such as examining effects on other processes and examining unloading operations with the new timing. To design and develop HDDs under extremely rapid technological development, rapid design and high flexibility are required. Accordingly, a technique is desired that increases frequency of fall check and unloads an actuator with more safety against a fall from a lower position without extensive modification of existing designs.